Cast 64 bit off_t to 32 bit size_t

Some systems have sizeof(off_t) == 8 while sizeof(size_t) == 4.
This implies that we are able to access and work on files whose
maximum length is around 2^63-1 bytes, but we can only malloc or
mmap somewhat less than 2^32-1 bytes of memory.

On such a system an implicit conversion of off_t to size_t can cause
the size_t to wrap, resulting in unexpected and exciting behavior.
Right now we are working around all gcc warnings generated by the
-Wshorten-64-to-32 option by passing the off_t through xsize_t().

In the future we should make xsize_t on such problematic platforms
detect the wrapping and die if such a file is accessed.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>

builtin-blame.c

@@ -1963,7 +1963,7 @@ static struct commit *fake_working_tree_commit(const char *path, const char *con
 				die("Cannot lstat %s", path);
 			read_from = path;
 		}
-		fin_size = st.st_size;
+		fin_size = xsize_t(st.st_size);
 		buf = xmalloc(fin_size+1);
 		mode = canon_mode(st.st_mode);
 		switch (st.st_mode & S_IFMT) {